Caterpillar Performance Handbook, January 2017, SEBD0351-47

Trenching Production ● Trenching RateWith Pipesetting ● Pipesetting Example Problem

Hydraulic Excavators

Trenching Production with Pipesetting On many sewer construction jobs the excavator does more than just dig the trench. Other tasks include han- dling the shoring system, placing bedding material, and lowering the pipe. The normal work procedure is to open a section of trench and then stop and make a pipe installation before going on to dig the next section of trench. At that point the key to trenching production is the total amount of time required to install each sec- tion of pipe. Pipe installation time can be broken down as follows: Digging time + other time = Total pipe installation time Total Pipe InstallationTime Pipe Installed Per Hour __________________________ _______________________ 60 min 1 Pipe/hr 30 min 2 Pipe/hr 15 min 4 Pipe/hr 10 min 6 Pipe/hr Digging Time can be calculated once the trenching rate has been calculated using the methods described earlier in this section. Once Digging Time has been calcu- lated, it can be added to an estimate of “Other Time” to determine Total Pipe Installation Time. “Other Time” can be estimated based on a contractor’s judgment, expe- rience, or actual measurement on a job. The following formula and table relate the trenching rate of the exca- vator to the time required to open a section of trench for pipe of various lengths. Pipe Length (ft) Digging Time (Min.) = ___________________ Trenching Rate (ft/hr) × 60 (Min/hr)

12' sections of pipe (1000 pipe to be installed). Excavator “A” can work at 60 ft/hr while Excavator “B” is capable of producing 120 ft/hr. Table shows that Excavator “B” will only take 0.10 hr to do the same work. This means that over the course of installing the 1000 pipe the more productive machine will save 0.10 hr/pipe or 100 hours of working time. Example problem (English) The following example shows how trenching produc- tion can be calculated on a job where the excavator is also required to set pipe. This example is based on the assumption that the excavator’s earthmoving rate and the pipe installation time have already been estimated by the contractor. Problem: Contractor estimates that the 350 Excavator will be able to produce 500 LCY/60 min. hr. Survey shows that an average cross section trench contains 3.2 BCY/ft and swell factor for sandy clay soil is esti- mated at 25%. How much trenching production can a contractor expect; assuming it takes 10.0 min. to install each 20 ft length of pipe after trench has been opened. Also assume 83% job efficiency — 50 min. work hour and 8 work hours out of a 9 hour shift. (0.5 hours for lunch and two 15 minute breaks.) Solution:

Convert trench volume to LCY/ft: 1.25 (3.2 BCY/ft) = 4.0 LCY/ft Convert Earthmoving rate to Trenching rate: 500 LCY/hr ___________ = 125 ft/hr 4.0 LCY/ft Calculate digging time for each pipe: 20 ft/pipe _________ = 0.16 hr/pipe = 9.6 min 125 ft/hr Calculate pipe installation time: Digging time = 9.6 min Other time = 10.0 min ________

Trenching Rate Ft. Per Hour 20 ft/hr 40 ft/hr 60 ft/hr 80 ft/hr 100 ft/hr 120 ft/hr 140 ft/hr 160 ft/hr 180 ft/hr 200 ft/hr

Time Required to Dig for Pipe ofVarious Lengths 8 ft Pipe 12 ft Pipe 16 ft Pipe 20 ft Pipe Hours Min. Hours Min. Hours Min. Hours Min. 0.400 24.00 0.600 36.00 0.800 48.00 1.000 60.00 0.200 12.00 0.300 18.00 0.400 24.00 0.500 30.00 0.130 8.00 0.200 12.00 0.260 16.00 0.333 20.00 0.100 6.00 0.150 9.00 0.200 12.00 0.250 15.00 0.080 4.80 0.120 7.20 0.160 9.60 0.200 12.00 0.060 4.00 0.100 6.00 0.120 7.20 0.167 10.00 0.057 3.43 0.086 5.14 0.114 6.86 0.143 8.57 0.050 3.00 0.075 4.50 0.100 6.00 0.125 7.50 0.044 2.66 0.067 4.00 0.089 5.33 0.111 6.67 0.040 2.40 0.060 3.60 0.080 4.80 0.100 6.00

Pipe Installation time = 19.6 min Calculate pipe installations/hour: 60 min/hr ____________ = 3.06 pipe/hr 19.6 min/pipe

Calculate max. pipe installations/day: 8 hrs (3.06 pipe/hr) = 24.48 pipe/day Actual pipe/day: 0.83 (24.48 pipe/day) = 20.3 – 20 pipe/day Actual feet/day: (20 pipe/day) × (20 ft/pipe) = 400 ft/day

This table can be used to show how an excavator that is capable of more trenching production will provide significant advantages even on jobs where the machine does not dig all of the time. Consider 12,000' job with

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